Phantom power, also called Vampire power, is power that's used by electronic devices even though they're powered off. I've also heard it's a big deal with various chargers being plugged into sockets, but their corresponding devices not being attached. For example, a cell phone charger left plugged into a wall should use power (and generate heat) even when the cell phone isn't plugged into it.
My son is a part of some high school groups that advocate peace and environmental awareness. He heard about this at school and came home to leave us this note:
It was pretty funny, and we agreed to work with him and unplug things in the kitchen we weren't using. However it's a pain and I decided to take my Kill-a-Watt and do some investigating. I was pleasantly surprised by the results.
Cell phone charger - My T-Mobile G-1 has a mini-USB plug, so most every charger works with it, including my wife's Blackberry chargers. I measured the load of a few chargers at rest, no cell phone plugged in, and they showed 0 watts (W).
I checked the blender, the electric kettle, and the toaster, all showing 0W when not being run.
This somewhat goes against the advice that I've heard, and even passed on before. I have some longer term tests across a few hours running to see if things change, but for now, it appears to me that the nuisance of unplugging and managing small devices isn't worth the trouble.
A Better close up as well: